High frequency amplifier circuit



1942- M. J} o. STRUTT ET AL 2,293,414

HIGH FREQUENCY AMPLIFIER CIRCUIT Filed Jan. 17, 1941 INVENTORS ATTORNEY Patented Aug. 18, 1942 FFICE 1 HIGH FREQUENCY AMPLIFIER CIRCUIT Maximiliaan Julius Strutt and Alder-t van der Ziel, Eindhov'en, Netherlands Application January 17, 1941, Serlal No. 374,804 In the Netherlands March 21, 1940 7 Claims. (Cl. 179-171) In our copending application, Ser. No. 333,088, filed May 3, 1940, there is described a high-irequency amplifier circuit comprising at least one amplifier valve whose cathode is provided with at least two leads, one 01' which, for the oscillations to be amplified, is included in the input circuit and another in the output circuit,and. in which capacities are connected between the control grid and the point of the cathode which is connected to the cathode lead included in the input circuit and between the control grid and that end of the cathode lead included in the output circuit which is not connected to the cathode,

and one or both cathode leads comprises or comprise impedances of which at least one has an inductive character, said capacities and impedances being proportioned in such manner that the input damping is approximately zero or negative.

The invention has for its object to provide means permitting of obtaining a further decrease of the input damping or the same decrease of the input damping by means of smaller values of the said capacities and impedances.

According to the invention, for this purpose the cathode lead included in the output circuit is coupled inductively to the input circuit in such a sense that a regenerative feedback occurs.

In order that the invention may be clearly understood and readily carried into effect it will now be described more fully with reference to the accompanying drawing, in which an amplifier circuit embodying the invention is illustrated, the supply sources being omitted for the sake of simplicity.

The drawing shows an amplifier valve l comprising a cathode 2 provided with two leads, a control grid 3, a screening grid 4, a suppressor grid 5 and an anode I. The high-frequency oscillations to be amplified are fed to an input oscillatory circuit l2 which is connected on the one hand to the control grid 3 and on the other hand, via one of the cathode leads, to the cathode 2. The anode l is connected to the cathode 2 via an output-oscillatory circuit l3, from which the amplified oscillations are taken off, and via the other cathode lead.

The cathode leads include inductances L1 and L2 and the point 8 of the inductance Li, which point is adjacent to the cathode, is connected to the control grid 3 via 'a capacity C1 and the end of the inductance L2 (9) which is remote from the cathode is connected to the control grid via a capacity C2.

The screening grid 4 is connected, via a ca-- pacity C3, to that end of the inductance In which is remoteirom the cathode so that the natural capacity between the control grid and the screening grid assists in the action of the capacity C2. The suppressor grid 5 is also connected to the Point 9.

If the elements L1, L2, C1 andC: oi the circuit described-so far are correctly proportioned this circuit permits of the input damping, which occurs due to the finite transit time of the electrons, being suppressed entirely so that the consequential input damping becomes zero or even negative. The elements L1, L2, C1 and C: can be formed in part but not all of them by the natural inductances oi the cathode leads and the natural tube' capacities.

According to the invention a further decrease of the input damping or the same decrease of the input damping is obtained at smaller values of Li, L2, C1 and C2 by inductively coupling the cathode lead included in the output circuit to the input circuit in such a sensethat a regenerative feed-back occurs. For this purpose the inductance L2 must be coupled to the input circuit, as may be eiiected by means of a mutual inductance Ml between the two cathode leads, by means of a mutual inductance Ma between the inductance L2 and the input oscillation circuit II, by means of a mutual inductance Ma between the inductance La and a supplementary inductance M included in the input circuit or by a combination of the said mutual inductances.

What we claim is:

1. A high=frequency plifier circuit comprising at least one amplifier valve having at least a control grid, an anode and a cathode, the latter being provided with at least two leads, one of which, for the oscillations to be amplified, is

included in the input circuit and another in the output circuit and in which intermediate the control grid and the point of the cathode which is connected to the cathode lead included in the input circuit and intermediate the control grid and that end of the cathode lead included in the output circuit which is not connected to the cathode are capacities and one or both cathode leads comprises or comprise impedances at least one of which has an inductive character, said capacities and impedances being proportioned in such manner that the input damping is approximately zero or negative, wherein the cathode lead included in the output circuit is coupled inductively tothe input circuit in such a sense that a regenerative feedback occurs.

5. A circuit for the amplification of high irequencies, comprising an electron discharge tube provided with at least a cathode, a signal input grid and an anode, the cathode. having at least two leads connected thereto, input and output circuits connected respectively to the input grid and to the anode, thegrid return of the input circuit being connected to one of the cathode leads, the plate return of the output circuit being connected to the other cathode lead, a pair of condensers each having one terminal connected to the signal input grid, the other terminal of one condenser being connected to the end remote from the cathode of one of the cathode leads, the other terminal of the other condenser being connected to the end adjacent the cathode of the other cathode lead, and mutual coupling between said cathode leads whereby regenerative feedback is produced,

6. A circuit for the amplification of high frequencies comprising an electron discharge tube provided with at least a cathode, a signal input grid, a screen grid and an anode, the cathode having a pair of leads connected thereto, an impedance connected to each of the cathode leads, input and output circuits connected respectively to the input grid and to the anode, the grid return of the input circuit being connected to the end remote from the cathode of the impedance connected to one of the cathode leads, the plate return of the output circuit being connected to the end remote from the cathode of theimpedance connected to the other cathode lead, a condenser connected between the signal input grid and the cathode end of the impedance included in the input circuit, capacitive means connected between the signal input grid and the end remote from the cathode of the cathode impedance included in the output circuit, and mutual coupling between the cathode impedance included in the output circuit and the input circuit whereby regenerative feedback is produced.

7. A circuit according to the invention defined in claim 6 wherein the mutual coupling is between the two cathode impedances,

MAXIMILIAAN JULIUS OTTO STRUTT.

ALDERT VAN DER ZIEL. 

